Study the effects of a Robinson wiggler at SOLEIL towards brightness increase

H. Abualrob, P. Brunelle, M. Labat, L. Cassinari, M.A. Tordeux, L. Nadolski,R. Nagaoka, A. Nadji, M.E. Couprie, O. Marcouillé

Outline• Synchrotron radiation & its properties

• Robinson wiggler & emittance reduction

• Experimental observation of Robinson effect @ SOLEIL

• Predicted influence of a Robinson wiggler on the spectral performances

• Preliminary magnetic design of Robinson wiggler

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Light source

A bright photon beam is:Intense

Emitted from a small size and low divergence sourceMonochromatic

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BW) )(0.1%divergence size)(beam (beamfluxphoton Brightness

Synchrotron SOLEIL

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Energy 2.75 GeV

Circumference 354 m

Emittance H 3.9 nm.rad

Emittance V 39 pm.rad

Current 500 mA

Beam lifetime (bare machine)

15 h

beamlines 26

Spectral range IR to hard X-ray

Beam Brightness and emittance

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''

24%1.0/

zxzx

BWfluxB

)()(')( exexex

)()(')( phxphxphx

Effective electron beam emittance

Effective photon beam emittance

2)(,

2)(,, phzxezxzx 2

)(,2

)(,, '''''' phzxezxzx

Effective emittance is the beam size times the angular divergence

Beam size Beam divergence

high brightness low emittance

𝝈𝒑𝒉𝝈′𝒑𝒉e-

Energy spread & bunch length

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E

Number of electrons

Energy of electrons

EE

LL

Bunch length

in seconds

EfE

st

2

Energy spreadSynchrotron frequency

Momentum compaction factor

L

L+ΔL

EE

e

Energy spread

Emittance reduction: motivation

Spectroscopy• high spectral resolution• high flux through narrow slit Crystallography • high angular resolution• wavelength matching to crystal dimensions

High flux within small beam size and divergence

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High brightness low emittance (H & V)

Emittance reduction methods

• Increasing the number of dipoles: MAX IV S. Leemans, Phys. Rev. Spec. Topics AB 12, 120701, 2009.

• Introducing a transverse gradient in the dipoles: ALBA D. Einfeld, Status of ALBA project, IPAC10, Japan.

• Installing tens of meters of damping wigglers: PETRA III M. Tischer, Damping wigglers for PETRA III light source, proceeding PAC05, Knox ville, Tennessee.

• Installing a Robinson wiggler

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Robinson wiggler

Compact, less expensive, can be adopted by compact & large machines

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00

wL

dsdxdBB

Parameter Equation present With Robinson wiggler

Damping partition

Horizontal emittance

Energy spread

0D 1D

20x

Dxx

11

0

0

02EE

wL

x dsdxdBB

BD

02

00

0

)(

0x

0

0

EE

2

0

02

22

EDEEE

sx

B dB/dx<0 B dB/dx<0B dB/dx<0B dB/dx<0

Robinson wiggler: magnetic system of alternated field gradient superimposed to the main field, to be installed in a non-zero dispersion straight section (1)

(1) K. W. Robinson, Radiation effects in circular electron accelerators, physical review, vol. 111, number 2, 1958.

Previous projects

• First observation @ Cambridge Electron Accelerator (CEA)

A. Hofmann, Design and performance of the damping system for beam storage in the CEA, ICHEA, Cambridge, 1967.

• Installtion in the PS @ CERN showing 50% horizontal emittance reduction

Y. Baconnier et al, Emittance control of the PS e+/e beams using a Robinson wiggler, Nucl. Instr. and Meth. in Physics Research A234 (1985) 224-252.

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Experimental study of Robinson effects on:

-The horizontal emittance-The energy spread @ SOLEIL

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Robinson effect @ SOLEIL • Presently, there is no Robinson wiggler

@ SOLEIL ! IDEA…

• Use the 4 undulators U20 to obtain a strong periodic magnetic field

• Simultaneous off-axis propagation in the 4 undulators to create a periodic field gradient

• Measure the transverse beam size using a pinhole camera

• Measure the bunch length using a streak camera

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e-

The in vacuum undulator U20

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Gap 5.5 mm

Bmax 0.97 T

K 1.8

Period length 20 mm

No. of periods

98

Beam size measurement to deduce the emittance variation

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0

0

x

xxx

Beam size measurement using a pinhole camera

Bunch length measurement to deduce the energy spread variation

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0

00

0

E

EEE E

EEE

Bunch length measurement using a

streak camera

Emittance reduction, energy spread increase & spectral performances with a Robinson wiggler

• Assuming that a Robinson wiggler is installed @ SOLEIL

• Assuming horizontal emittance reduction by a factor of 2 (from 3.9 nm rad to 1.95 nm rad)

• Assuming energy spread increase by (from 1.01 10-3 to 1.428 10-3)

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2

Photon flux calculation/low energy range

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Undulator HU640

Type Helical/EM

Period (mm) 640

Bz (T) 0.15

K 8.9

Flux calculation with SRW (1) through an aperture of 0.1 * 0.1 mm2 located @ 10 m from the source(1) O. Chubar, Accurate and efficient computation of synchrotron radiation in the near field region, EPAC 98, Stockholm.

Photon flux calculation/high energy range

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undulator U20

Type planar/PM

Period (mm) 20

Bz (T) 1.08

K 2

Flux calculation with SRW through an aperture of 0.1 * 0.1 mm2 located @ 10 m from the source

19

Brightness calculationBrightness decrease for low

energy range (HU640)

90% Brightness increase for high energy range (U20)

''24

zxzx

fluxB

Remember that

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Robinson wiggler...preliminary magnetic design

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Gap 6 mm

Bmax -2.5 T

193 T2

Period length 164 mm

Wiggler length 2 m

dsdxdBB z

Design performed using RADIA code. O. Chubar, Computing 3D magnetic fields from insertion devices, PAC 1997, Vancouver, Canada.

e-

Conclusion

• Robinson effects on reducing the emittance and increasing the energy spread were observed and validated experimentally, for the first time, in a synchrotron light source at SOLEIL.

• Considering a Robinson wiggler at SOLEIL reduces the emittance, leading to brightness increase “in the high energy range”. However, Robinson wiggler increases the energy spread leading to flux reduction.

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Thank you for your attention

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